A human B-cell line expressing immunoglobulin receptors specific for the Forssman antigen has been established in long-term culture. This cell line which has a normal human female karyotype, was derived from a peripheral blood lymphocyte. In order to establish additional antigen-binding B-cell lines at various stages of differentiation, B-lymphocyte hybrids are to be generated by the fusion of antigen-primed human splenic lymphocytes to one of several currently available neoplastic B-lymphomas. Seven human B-cell 8-azaguanine resistant sublines have been established for use in these fusion experiments. The antigen-binding B-cell line and the B-cell hybrids will be used to study several membrane events which occur following the cross-linking of receptors with either antigen or anti-idiotype reagents. An attempt will be made to link these events with cell function. In particular, we shall investigate antigen- and mitogen-induced differentiation of the human B-cell lines. Several parameters of differentiation are to be monitored including: isotype switching Mu greater than Delta greater than Gamma; loss of immunoglobulin receptors; induction of immunoglobulin secretion; change (acquisition or loss) of the expression of two B-cell differentiation antigens B-1 and B-2; and a change in ultrastructural morphology from lymphocytic to plasmacytic. During these studies we shall also attempt to define the role that various lymphocytes (B-cell T-cell) or lymphocyte monocyte factors play in B-cell differentiation. Both conventional and monoclonal antibodies specific for selected membrane macromolecules from the B-cell line and B-cell hybrids will be screened in an attempt to identify new serologically-defined B-cell differentiation antigens. The biochemical characteristics and functional signigicance of these B-cell markers will be investigated. Particular emphasis will be given to the identification of a marker associated with the putative antigen-specific memory B-cells.